Caption: Microbiology analysis. Scientist working for the UK's Health Protection Agency (HPA) preparing microbial cultures in petri dishes. Culturing and studying such samples allows bacterial and fungal diseases to be diagnosed and treated. The nutrient medium being used in these petri dishes is XLD (xylose lysine deoxycholate) agar, used to culture Salmonella and Shigella bacteria. This work is being carried out at the HPA's Centre for Infections.